KappaLite 3015 in Ashdown ABM 115 Cab

Hi, I've just replaced the Blueline Sica driver in my roughly 5 year old Ashdown ABM 115 deep cab with an Eminence Kappalite 3015. Considering the price, specs, reviews etc I was expecting a bit more, specifically more controlled bottom end - its starts to sound like it's struggling with the lower notes much as the Blueline speaker did except it doesn't "fart".
I was wondering if changing the port tuning would improve matters. I did a "Rice Test" and the rice stopped jumping around at 37hz - is this likely to be how Ashdown factory tuned it or is this as a result of changing the driver? I've looked at the cabinet designer on the Eminence website and it suggests a box of 5 cu.ft whereas mine is about 4.6 cu.ft. It suggests 2 x 4" by 3.5" ports whereas mine has 2 x 3" by 3.5" ports. It recommends tuning to 42 hz.Phew...!

My question is should I alter the port tuning to achieve 42hz as per the eminence design. If so should I shorten the existing 3" ports or would I be better fitting longer 4" ports and shortening until the "rice test" gives the desired result. I don't really want to be cutting new holes and getting bigger ports unless the benefits are worth it - if that's the sound the box gives me perhaps I need a bigger box!
I'm using a 77 Jazz into an Ashdown ABM 500 EVO, any help would be much appreciated!

Cheers for the reply - do you think it's worth trying 4" ports then? I can't really go back if they don't work!

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If there is a place to put it, maybe going with one extra rear facing port that will be scaled to provide the eminence suggested tuning.
If you don't like it you can just put a big cork in it, or find the sort of port Trace Elliot used to use with an optional screw on bung.

Cab size is so close to recommended you can be sure it will work with a tuning close to the Eminence tuning. The predicted tunings from winISD vary from Eminence proven design but you can interpolate 4" port length for your slightly smaller box.

Eminence might actually tell you if the extra rear port is a good plan. They are very good at helping out customers.